do a search on my posts. depends on what you want to do with it. I have a stock rb26dett with 680cc injectors and 15psi booste and i cant get it out of the hole (drag racing) with breaking something in the rear end. the 2 options im considering is grafting a gtr rear suspension or a for 8.8 or 9 inch rear end. plain and simple you will not be able to mod the stock IRS to handle good traction hi HP launches at the track. if you plan on only street use an r-200 with cv upgrade will work. i went as far as maching my rear struts to accept bigger bearing for the 300z z31 stub shafts, custom chomoly axles and a nismo r-200 LSD. the diff and axles are good now i just broke a stub shaft;< again anything other then drag racing this setup would be greawt ;> good luck.
BTW if you have the car stripped id go with a 9 inch ;>